it was probably your original assumption that a secondary injector wasn't firing.
if it's still together you can check the injector continuity by accessing the ECU, turn the key on and backprobe each of the 4 injector wires to see if they all read close to 12v.
but live and learn, you knew it was running lean but decided to push it anyways. why would you have a wideband but no boost gauge?
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